Inductive position sensors are used, for example, as rotary encoders to determine the angular position of two machine parts rotatable relative to each other. In inductive position sensors, excitation coils and receiver coils, for instance, in the form of printed conductors, are applied to a shared printed circuit board that is firmly joined to a stator of a rotary encoder, for example. Disposed oppositely to this printed circuit board is a further board often in the form of a graduated disk, on which electrically conductive and non-conductive surfaces are applied so as to alternate at periodic intervals as graduation region or graduation structure, and which is joined in torsionally fixed fashion to the rotor of the rotary encoder. When an electric excitation current changing over time is applied to the excitation coils, signals which are a function of the angular position are generated in the receiver coils during the relative rotation between rotor and stator. These signals are then further processed in evaluation electronics.
In addition, inductive position sensors are also frequently used for the direct measurement of longitudinal shifts along an axis. In so doing, the same measuring principle is used as for the rotary encoders indicated above, however, the receiver coils and the graduation structure then extend along the straight-line axis.
Inductive position sensors of this type are often used as measuring devices for electric drives to determine the relative movement or the relative position of corresponding machine parts. In this case, the position values, which are generated by the position sensors, are supplied via a suitable interface arrangement to sequential electronics for controlling the drives. Such a configuration, made up of position sensor, interface arrangement and sequential electronics, is denoted as a measuring system.
In many fields of application of such position sensors and measuring systems, there is the continuous desire that they satisfy safety-related requirements. Often, it must be possible for persons to be allowed to stay within a swiveling range of machine parts whose drives interact with the measuring system. Under these conditions, it is necessary to preclude these persons from getting into danger due to faults in the measuring system. Correspondingly, the possibility that material goods in the vicinity of the moving machine parts could be damaged should naturally be avoided at the same time.
In German Published Patent Application No. 197 51 853, an inductive position sensor is described in which the receiver coils are disposed within one track with a displacement that brings about a 90° phase shift of the received signals. In general, a failure of a receiver coil or a fault in the evaluation electronics would not be discovered.
Japanese Published Patent Application No. 2004-205456 describes an incremental encoder that generates three signals phase-shifted by 120°. However, a corresponding encoder does not satisfy higher safety-related requirements.